Conventionally, a balance communication system for carrying out data transmission by use of a pair of transmission lines which are in a balanced status has been used widely. In this kind of the balance communication system, there are many cases in which a transmission line by use of a dedicated communication line etc. such as a telephone line, is used, and normally, a certain level of balancing is kept,
One example of a transmission section and a transmission line of a conventional balance transmission apparatus is shown in FIG. 28. This balance transmission apparatus is configured so as to send out a signal from a transmission section 91 to a transmission line which is composed of a pair of conductors W1, W2, through a transmission transformer T92. At this time, a current of a transmission signal which is sent out from the transmission section 91 is dependent on characteristics of the transmission section 91 and the transmission lines W1, W2.
It is required that a transmission line leading from a transmission section to a reception section is completely balanced by nature, but in a practical sense, there are unbalance elements in the transmission section and the reception section, and unbalance components etc. due to a status of wiring on a transmission path and a device which is connected in midstream, and an actual condition is that it is not possible to say that currents, which flow through the conductors W1; W2 as the transmission line, are balanced completely. In this manner, when a current flowing through a transmission line is unbalanced, a part of electric power is leaked from the transmission line to outside, and there occur such problem that a transmission characteristic of data is deteriorated and interference is generated, and so on.
In recent days, such a balance communication system that a high frequency signal is overlapped with an electric power line for feeding electric power such as a commercial power source to carry out data transmission has been proposed. Especially, the suchlike electric power line is not a communication line by nature, and therefore, there is such a case that balancing fluctuates, depending on a wiring status in individual house, a device which is connected to a power source, and so on. On this account, there is such fear that, in case that an electric power line is used as a transmission line, balancing is changed by individual environments, and a transmission characteristic differs substantially.
Patent Document 1 describes a balance transmission apparatus which detects an unbalance component from a voltage or current of a conductor on a transmission side or a reception side, and carries out transmission control in such a manner that the detected unbalance component gets smaller.
However, Patent Document 1 does not describe about a concrete method for detecting an unbalance component.
[Patent Document 1] JP-A-2004-140565 publication